In subsurface drill-rig applications where diamond drilling methods are used to extract core samples during exploratory or directional drilling, it is essential to determine the orientation and survey position of each core's position underground before being drilled out and extracted. The purpose of this is to be able to produce a three dimensional ‘map’ of underground mineral/rock content. This is applicable to Mining, Oil & Gas exploration, Directional Drilling and Civil Engineering industries.
Current technologies use Core-Orientation units attached to core inner tubes and back-end assemblies to determine the correct orientation of the drilled out core sample after a preferred drilling distance, such as every 1.0 meter, 1.5 meters, 3.0 meters or 6.0 meters of drilling. These core orientation units measure rotational direction of the core sample before extraction. On retrieval at the surface of the hole, the rotational direction can be determined by electronic means and the upper or lower side of the core material physically ‘marked’ for later identification by geologists.
In addition, at periodic depths, say, 30 meter drilling intervals, a ‘Survey Instrument’ is lowered down the drill hole to determine azimuth (angular measurement relative to a reference point or direction), dip (or inclination) and any other required survey parameters. These periodic depth survey readings are used to approximate the drill-path at different depths. Together with the rotational position of the extracted core (from the core orientation device), the subsurface material content map can be determined.
The survey instruments, if utilising magnetic measurement components to determine azimuth (e.g. magnetometers), will be at least 3 meters from any significant metal parts having magnetic influence that might otherwise affect measurements by the probe's instruments. For example, ferro-metallic drill bit or any section of steel inner or outer tubes which make up the ‘drill-string’. This is to ensure that the survey measurement is not corrupted by being in proximity to metallic material which could cause erroneous azimuth data readings. To achieve this requirement, the survey probe is inserted through the circular centre open section of the drill bit while the outer drill tube (attached to the drill bit) is raised three or more meters above the survey instrument to allow it to capture accurate azimuth data. To be positioned three or more meters below the drill bit and tubes, the survey instrument needs to be further attached to a series of aluminium rods (non-magnetic influence material) to achieve the distance separation.
The entire process as described above is considerably time consuming having to re-insert survey instruments every 30 meters while pulling back the drill string, removing and extracting data from both the core orientation and survey instruments and the need to assemble/disassemble mechanical fixtures to initiate start of operation and to read data from the instruments after extraction from the drill hole. There is also a need for substantial capital investment or lease/hire arrangements for the extra equipment needed on site.
It has been found desirable to provide an improved method and apparatus for obtaining downhole data without the need to insert a survey probe to measure azimuth and inclination/dip of the drillhole path.